Apparatus with a chemical indicator for indicating exposure to an oxidative sterilant or disinfectant

ABSTRACT

An apparatus for determining exposure to an oxidative sterilant is described. The apparatus includes a chemical indicator for indicating exposure to the oxidative sterilant and a biological indicator for determining the effectiveness of the exposure to the oxidative sterilant. The chemical indicator has a metallic surface with a non-pH sensitive permanent indicator on the surface for indicating exposure to the oxidative sterilant. The chemical indicator may be on a self-contained biological indicator. The biological indicator and chemical indicator may be inside a test pack, where the test pack restricts sterilant flow to the indicators.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.09/290,592, filed Apr. 13, 1999, now U.S. Pat. No. 6,218,189 which is acontinuation of U.S. application Ser. No. 08/966,397, filed Nov. 7,1997, now U.S. Pat. No. 5,942,438.

FIELD OF THE INVENTION

The invention relates to an apparatus including a chemical indicator forindicating exposure to an oxidative sterilant and a biological indicatorfor determining the effectiveness of exposure to the oxidativesterilant.

BACKGROUND OF THE INVENTION

A variety of medical instruments are used for the diagnosis andtreatment of medical ailments. Transmission of microorganisms to apatient from a medical device can result in a serious disease or death.The medical instrument used to treat the medical ailment is preferablyfree of microorganisms which thereby minimizes the spread of disease orinfection to the patient. A method of sterilizing medical instrumentscomprises providing an oxidative sterilant or disinfectant in the formof liquid, gas, or gas-plasma to a sealed chamber housing the medicalinstruments. One sealed chamber type device is the STERRAD®Sterilization System available through Advanced Sterilization Productsof Irvine, Calif., a division of Johnson & Johnson Medical, Inc.Providing the sterilant in gas or plasma form (hereinafter “gas”) isespecially desirable because the gas renders the surface of the medicaldevice sterile, thereby rendering viruses and bacteria harmless.Likewise, the gas spreads to enclosed or isolated areas of the medicalinstrument which would otherwise not be sterilized. After a period oftime the sterilant in gas form render the devices sterile and a medicaltechnician removes the medical instruments from the chamber.

The importance of achieving complete sterilization motivates placing anindicator in the chamber with the medical instruments to provideverification that an adequate amount of sterilant was provided to thechamber. The prior art method of verifying if the sterilant had enteredthe chamber comprised placing a chemical indicator and a biologicalindicator in the chamber. A chemical indicator comprises a surfacehaving a chemical thereon which changes color upon exposure to asterilization process. Chemical indicators are often integrated withother sterilization verification devices to provide additional evidenceof exposure to sterilant. Biological indicators are packages whichcontain a high number of bacterial spores. The biological indicator,after being exposed to sterilant, is culture tested to determine if thebacteria are viable. If the sterilization was successful, the bacteriacontained within the biological indicator will not grow.

In general, chemical indicators should satisfy several basic performancecharacteristics. The chemical indicator should be readable, reliable,selective, stable, and safe. These performance characteristic areexplained in more detail in Volume 1 of the Sterilization StandardsCommittee of the Association for the Advancement of MedicalInstrumentation (AAMI) and by the General Requirements for ChemicalIndicators of the proposed American National Standard Institute (ANSI)drafted by Chemical Indicators Working Group. These two documents areincorporated herein by reference.

Chemical indicators of the prior art generally comprise a pH-sensitivematerial placed on a medium. Simply, the pH-sensitive chemical indicatorchanges color when exposed to an acidic oxidation-type sterilant, suchas H₂O₂ or H₃CCOOOH, for a sufficient amount of time. The color changeoccurs from a chemically induced pH change, i.e., from basic to acid.For example, exposure to an acidic oxidation-type sterilant can changethe color of a pH-sensitive chemical indicator from blue to yellow orcolorless or from red to yellow. The pH-sensitive chemical indicators ofthe prior art can also be placed within containers known as test packs.A test pack is a structure which provides a challenge to thesterilization process and thereby provides a more realisticrepresentation of actual conditions of certain areas on medical devices.

The pH-sensitive chemical indicators of the prior art suffer fromseveral disadvantages and may not fully satisfy basic performancecharacteristics related to stability and selectivity. Since pH-sensitivechemical indicators are chemically reversible, their processed andunprocessed colors can change upon exposure to certain chemicals,especially those with acidic or basic characteristics. Poorpre-processing color stability of pH-sensitive chemical indicators ofthe prior art is undesirable because it requires chemical indicators tobe discarded after a relatively short shelf life thereby wastingsupplies. Furthermore, a chemical indicator of the prior art which is onthe verge of changing color due to chemical instability does not providean accurate chemical exposure indication when utilized in asterilization chamber. Additionally, a short pre-processing shelf lifefor the chemical indicator is even more undesirable when the chemicalindicator is integrated with a biological indicator because an even moreexpensive device (test pack, including chemical indicator and biologicalindicator) must be discarded when the pH-sensitive chemical indicatorchanges color.

Poor post-processing color stability of pH-sensitive chemical indicatorof the prior art is also undesirable because the chemical indicator willreturn to its original color if exposed to a base and, thus, theprocessed chemical indicator cannot be used as a permanent record of thesterilization process. Therefore, if exposed to a base, the chemicalindicator will revert to the original color and provide an unprocessedappearance. This characteristic of pH-sensitive chemical indicators ofthe prior art is particularly undesirable because using a chemicalindicator more than once may provide a faulty processing indication. Ina yet different scenario, the indicator could mislead a technician byproviding an unprocessed reading when, in fact, the load was processed.This would lead to repeated sterilization cycles thereby increasingcost.

Finally, the pH-sensitive indicators of the prior art are not veryselective and may change color upon exposure to any of a number ofreagents, not just oxidation-type sterilants. Thus, an indicator maychange color from exposure to an acidic reagent and not from adequateexposure to a sterilant. Such an inappropriate color change ismisleading and could lead to misinterpretation of result.

Another type of chemical indicator is disclosed in U.S. Pat. No.5,518,927 entitled “INSTRUMENT STERILIZATION [sic] LIFE-SPAN INDICATOR”to Malchesky et al. The Malchesky reference discloses using crystalviolet pigment sandwiched between two plastic members and attaching theplastic tag formed therefrom to an instrument during a sterilizationprocess. After repeated exposures, the pigment changes color. Based onthe color of the pigment sandwiched between the layers of plastic, thenumber of sterilizations, i.e. uses, which the instrument has undergonemay be determined.

The Malchesky reference discloses a chemical indicator which suffersfrom numerous disadvantages and drawbacks. First, crystal violet dyepossess pH-sensitivity at the extreme lower end of the pH scale. Infact, according to the Handbook of Stains, Dyes, and Indicators by FloydJ. Green, the visual-transition interval is pH 0.0 (yellow) to pH 2.0(blue-violet) using a 0.02% aqueous solution of crystal violet. Thus,since crystal violet dye is pH-sensitive, chemical indicators whichutilize crystal violet suffer from the same drawbacks as pH-sensitivechemical indicators of the prior art.

In response to these drawbacks, the Malchesky reference teachesenclosing the crystal violet dye in a plastic covering or tag to preventthe acidic sterilant from contacting the pH-sensitive crystal violetdye. However, enclosing the dye in plastic creates furtherdisadvantages. The first disadvantage is that the plastic tag is proneto simply falling off. Alternatively many medical instruments do notprovide a place to attach a tag, or if such a place it provided, the tagmay severely interfere with the operation and performance of the medicaldevice.

The Malchesky reference also teaches using crystal violet or otherorganic dyes. However, crystal violet, and many organic dyes in general,are toxic if released from their plastic cover. For example, crystalviolet, which has catalog number 229288 in the Sigma-Aldrich ChemicalCompany database, is a cationic triarylmethane dye, is toxic and maycause cancer, heritable genetic damage and irritate the eyes,respiratory system and skin. Thus, the invention of the Malcheskyreference suffers from another serious drawback.

Therefore, a need exists for a chemical indicator for use withoxidation-type sterilization systems which does not chemically breakdown, has increased sensitivity and will not give false indications uponexposure to common chemical compounds and conforms with the performancecharacteristic of the AAMI Sterilization Standards Committee. Thepresent invention satisfies that need.

SUMMARY OF THE INVENTION

One aspect of the invention involves an apparatus for determiningexposure to an oxidation-type sterilant or disinfectant. The apparatuscontains a biological indicator for determining the effectiveness ofexposure to the oxidation-type sterilant and a chemical indicator forindicating exposure to the oxidation-type sterilant. The chemicalindicator includes a metallic surface and a non-pH sensitive indicatoron the surface for indicating exposure to the oxidation-type sterilant.

Advantageously, the indicator is an azo dye. Preferably, the indicatoris a permanent indicator. In an embodiment, the surface is anodizedaluminum. Preferably, the surface includes a chromate conversioncoating. Advantageously, the biological indicator is a self-containedbiological indicator. In an embodiment, the chemical indicator includesa generally flat disk on the self-contained biological indicator. Theapparatus may also include a test pack, where the test pack isconfigured to provide for gas flow into the test pack by diffusion andwhere the chemical indicator and the biological indicator are insidesaid test pack. Advantageously, the apparatus includes a containerhaving a cover, where the cover is secured to the container with atamper-evident device, where the surface with the non-pH sensitivebleachable dye is on the tamper-evident device.

In an embodiment, the metallic surface includes a flexible medium havingthe indicator on the surface of the flexible medium. Preferably, theapparatus includes adhesive on the opposite side of the flexible mediumthan the indicator. The apparatus may also include a warranty indicatorwhich provides notice when the warranty of the apparatus is still ineffect. Advantageously, the oxidation-type sterilant includes hydrogenperoxide. Preferably, the hydrogen peroxide is aqueous hydrogenperoxide. Advantageously, the hydrogen peroxide is hydrogen peroxidevapor or gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a form of a self-contained biological indicatorhaving a chemical indicator portion comprising bleachable dye.

FIG. 2 illustrates a test pack incorporating a chemical indicatorcomprised of bleachable dye.

FIG. 3 illustrates a container having a tamper-evident deviceincorporating a chemical indicator comprised of bleachable dye.

FIG. 4 illustrates a flexible medium or tape incorporating a chemicalindicator comprised of bleachable dye.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention comprises a chemical indicator for oxidation-typesterilization processes. This invention provides a new type of chemicalindicator comprising a bleachable dye which permanently changes colorupon exposure to an oxidizing or bleaching sterilant. Advantageously,the present invention does not suffer from the drawbacks of the priorart. First, the dye on the chemical indicator is chemically andenvironmentally stable thereby increasing shelf life. Second, the dye isgenerally not pH-sensitive and hence will not undergo color change ifaccidentally exposed to a base or acid. Third, the claimed chemicalindicator is more versatile than chemical indicators of the prior art,because it can be manufactured to change color after a single exposureto sterilant or after multiple exposures to sterilant. Likewise, thisnew chemical indicator is selective to certain oxidation-type sterilantsand does not change color upon exposure to steam, water, light or otheracidic or basic compounds. Furthermore, the permanent color changeprevents the chemical indicator from reversing color after asterilization process. Finally, cytotoxicity test results indicate thatthe processed and unprocessed chemical indicators claimed herein arenoncytotoxic and pose no safety risk to the users.

The bleachable dye is a chemical composition comprising anon-pH-sensitive dye which upon exposure to an oxidation-type sterilantchanges color due to oxidation. Preferably, the dye comprises an azodye. More preferably the dye comprises a metallic azo dye integrated ona metallic surface through an anodization or chromate conversionprocess. Many different types of metallic azo dyes exist, including, butnot limited to the following:

Aluminum Bordeaux R

Aluminum Bordeaux RL

Aluminum Fiery Red ML

Aluminum Orange 3A

Aluminum Yellow 4A

Aluminum Yellow G3LW

Aluminum Green LWN

Aluminum Violet CLW

Aluminum Brown BL

Aluminum Olive Brown 2R

Aluminum Grey BL

Aluminum Black BK

Aluminum Gold S

The above list of dye is not exhaustive and is provided by way ofexample. Other azo dyes likely exist and are covered by the scope of thepresent application. Likewise, although the preferred embodiment isrealized utilizing metallic azo dyes, it is contemplated that othertypes of bleachable dyes could be used interchangeably. In the preferredembodiment described herein the substrate comprises aluminum, or analloy thereof. However, it is contemplated that other metallic basematerials, such as stainless steel, titanium, and other alloys can beutilized for substrate material. Likewise, it is also contemplated thatother, nonmetallic materials may serve as substrate material. Thesematerials include plastic, paper, cellulose-based fabric, andfiberglass.

The oxidation-type sterilants are of the type commonly used insterilization system, such as the STERRAD® Sterilization System made byAdvanced Sterilization Products of Irvine, Calif. The sterilants whichare contemplated for use with the chemical indicators claimed hereininclude, but are not limited to, chlorine dioxide, ozone, hydrogenperoxide, and peracetic acid. Other sterilants which effect a colorchange in the dyes described herein are also operable with the presentinvention.

The process of manufacture, described in more detail below, comprisesplacing the dye on or integrating with the anodization or chromateconversion coated surface on an aluminum substrate. The surface acts asa carrier for the dye and is preferably semi-permeable thereby providingfor the dye and sterilant to penetrate the surface or structure.Advantageously, integration of the dye with the metallic surfaceprevents the dye from rinsing or washing out of the chemical indicator.

In addition to the application for a single cycle process indicator,this manufacturing capability makes the dye also suitable for use as alimited re-use indicator or as a warranty expiration indicator.

Five primary factors control the number of exposures or amount ofexposure time required to change the color of the dye. The first factoris the amount of time that the dye is exposed to the surface. The secondfactor is the porosity and thickness of the layer on which the dye isplaced. The third factor is the oxidation resistance of the dye. Thefourth factor is the degree to which the surface is sealed usingsealant. The fifth factor is the concentration of oxidant and exposuretime to which the dye is exposed. Other factors beyond those enumeratedalso effect the rate of color change, although not as significantly asthe five enumerated above. The five factors are discussed in more detailbelow. The process for applying the bleachable dye to a surface dependsupon the surface to which the dye is applied and the intended use of theindicator created therefrom.

One material that is often used to construct medical instruments isaluminum alloy with either an anodized coating or a chromate conversioncoating. One form of aluminum alloy which may be used is 5052-H32although other types of material are covered by the inventive scope ofthe present invention. The anodized aluminum or chromate conversionlayer creates a particularly desirable surface in which to impregnatethe dye because both coatings have a porous surface layer which absorbsthe dye. The dye becomes stable in the upper surface of either layerthereby securing the dye during standard washing or handling yet allowsthe gaseous oxidizing sterilants to penetrate the porous surface tothereby bleach or oxidize the dye to a different color.

Method of Manufacture

A six step process is utilized to form the chromate conversion coatedaluminum. The six steps are cleaning, coating, rinsing, dyeing, rinsingand drying. Cleaning removes any oils that remain on the aluminum aftermachining and/or fabrication, de-oxidizes the surface and removes anylight oxide film to thereby ensure that the dye absorbs evenly. Cleaningis performed by a series of acidic, basic, and de-oxidizing rinses. Thesteps and the details described herein first comprise washing thealuminum. Washing comprises exposing the aluminum to inhibitednonetching alkaline soap at a concentration of 5-6 ounces per gallon at140-150° Fahrenheit (F.) and upon completion rinsed with water. Next,the surface is rinsed with nitric acid having a concentration of 20-25%by volume at a temperature of 140-150° F. The surface is rinsed withwater before being etched with caustic soda at a concentration of5.5-6.0 ounces per gallon and a temperature of 145-150° F. The surfaceis rinsed again to remove any excess caustic soda. Finally, the surfaceis exposed to a de-oxidizer to remove any unwanted oxidation. Thede-oxidizer is at a concentration of 16 ounces per gallon.

The second step comprises chromate coating. The chromate coat stepcomprises exposing the surface to Iridite 14-2 by dipping for 90 to 180seconds thereby forming a chromate conversion coat on the surface of thealuminum alloy. The Iridite 14-2 is at a concentration of 12 grams perliter at a temperature of 70-95° F. Witco Chemical Corporation atMelrose Park, Ill. provides Iridite 14-2 and instructions for its use.

The third step comprises rinsing the chromate conversion coated aluminumwith cold running water. This removes any impurities from the surfaceprior to dyeing.

Fourth, the coated aluminum is immersed in an aqueous dye solutioncontaining Bordeaux Red, which has the trade name Aluminum Bordeaux RLpowder, for 180 to 240 seconds at a temperature of 130-135° F. The dyehas a pH of 3.0-3.5 and is mixed at a concentration of 16 grams perliter. The dye is provided by Clariant Corporation located in Charlotte,N.C. Dyes of various colors may be used, however, the color red, whichbleaches to a yellow/gold color, advantageously maintains coloruniformity with chemical indicators of the prior art. Advantageouslyother types and colors of dye are compatible with the apparatus andmethod described herein. Alternative methods of applying the dye alsoexist and including, but are not limited to, spraying, a moving liquidbath, brushing, or dipping.

The fifth step comprises rinsing the surface with cold running water.This step removes any excess dye and permanently sets the dye that isabsorbed by the surface of the coated aluminum alloy. Of course, othermethods of rinsing are available, such as agitation, spraying, spinning,or dipping in standing or running water.

Finally, the surface of the colored aluminum is air dried. As known bythose of ordinary skill in the art, other methods of drying exist andare acceptable for use in the process described herein.

Also known by those of ordinary skill in the art is that the parametersof the above described process may be altered while still creating asurface having bleachable dye thereon which changes color upon exposureto an oxidation-type sterilant.

Sealed Anodized Aluminum

Another method and configuration of integrating a bleachable dye to asurface comprises dyeing and sealing anodized aluminum. This method andapparatus may provide another composition of bleachable dye indicatorbesides the chromate conversion coated aluminum described above.

The process for fabricating anodized aluminum containing a dye comprisesfirst anodizing the aluminum surface on a medical instrument to form anoxide film. Next, the surface is immersed in a dye bath which causes theoxide film to absorb the dye to become colored. The final step is toseal the surface in a bath of hot water or solution of sealing salts.The process for preparing dyed anodized aluminum is known by those ofordinary skill in the art and is shown in U.S. Pat. No. 5,658,529 issuedto Feldman and Hui, which is hereby incorporated by reference in itsentirety herein.

Furthermore, the azo dye surface combination of the present inventionmade according to the above method of manufacture provides a permanent,nonreversible chemical indication. This overcomes the disadvantage of pHindicators which reverse color upon exposure to a base reagent. Forexample, crystal violet is pH-sensitive, i.e. changes color, whenexposed to reagents having a pH of 0 to 2.5. Alternatively, the azo dyesof the present invention are generally not pH-sensitive and haveresistance to color change even when exposed to reagents having a pH of1 to 14.

Controlling the Rate of Color Change

As discussed briefly above, there are a number of ways to control therate of color change, which is to say the number of exposures to astandard sterilization process before the dye changes color. The rate atwhich the dye changes color depends on the concentration of thebleaching agent to which the dye is exposed, the amount of time the dyeis exposed to the surface, and the characteristics of the dye and thesurface. When the concentration of the oxidation-type sterilant and theduration of the sterilizing process are known and fixed, such as in asterilization chamber, the rate of change of the dye can be adjusted bycontrolling the factors listed above. When these controlling factors arealso held constant, the rate of change for a particular sterilizationprocedure is known. Accordingly, a surface containing dye can bemanufactured to change color after a predetermined number ofsterilizations. This characteristic is especially desirable for use asan indicator for limited re-use devices or as a warranty expirationindicator, both of which are described below.

The factors which may be controlled during the processing stage in theproduction of a surface having bleachable dye thereon are the dye color,dye concentration, thickness, and porosity of the anodized or chromateconversion layer, alloy composition, anodization bath characteristicsand sealant. A brief explanation for each of these factors follows.

Color of the Dye

Different dyes change color at different rates. Thus, by selecting a dyehaving a different color the number of sterilizations which must beundergone before the dye will change color can be controlled. Thisadvantageously also provides a visual indication of the service life ofan instrument, i.e., a color coded chart could be used to determineservice life such that the color red indicates a service life of 10uses, the color blue indicates a service life of three uses, etc.Advantageously, the bleachable dyes described herein are available in awide range of colors including black, red, blue, green, yellow, gray andbrown.

Concentration of the Dye

Likewise, the concentration of the dye will alter the degree ofbleaching that occurs when the dye is exposed to an oxidation-typesterilant. Use of a high concentration dye mixture decreases the rate ofcolor change. Applying dye in a low dye concentration mixture increasesthe rate of color change. Similarly, the length of time the dye isexposed to the surface will affect the amount of dye absorbed by thesurface and accordingly will effect the rate of color change of thesurface. If the dye is exposed to the surface for a long period of timethen the surface will absorb more dye and color of the surface willchange at a slower rate when exposed to an oxidizer.

Composition of the Surface Layer

The composition of the alloy will also affect the bleaching process. Oneof the primary reason for the difference in the rate of color changebetween different alloys is based on the porosity of the material, i.e.the material's ability to absorb the dye and the ability of thebleaching agent to penetrate the material during sterilization.Compositions of matter which are acceptable include, but are not limitedto, anodized aluminum, chromate conversion layers or other such porussurfaces. It is also contemplated that other surface layers arecompatible with the invention described herein.

Thickness of the Surface Layer

Controlling the thickness of the anodized or chromate conversion layer(hereinafter “layer”) also controls the rate of color change. A thicksurface layer will maintain the original color for a longer period oftime then a thin layer. This occurs because a thick surface layercontains more dye than a thin surface layer and consequently thesterilant takes more time to penetrate the surface to reach the dye.Similarly, the application of the layer will also effect the behavior ofthe layer. For example, changing the chemical composition of theanodization or chromate conversion bath and/or the amount of electricalcurrent used during the anodization process will affect the structure ofthe layer, which in turn effects the rate of color change of the dye.Anodizing aluminum and applying a chromate conversion layer are known bythose of ordinary skill in the art, and accordingly not described ingreat detail herein.

Utilization of a Surface Sealant

Finally, placing a sealant over the surface will decrease the rate ofcolor change of the dye contained thereunder. Accordingly, varying theamount and type of sealant will affect the characteristics of the dye.Various types of sealants exist and include but are not limited to water(hydration) or nickel compounds. Preferably, Anoseal 1000 type sealantfrom Noamax Technologies in Atlanta, Ga. is used as the sealant tocontrol the rate of bleaching.

In Operation

To use a chemical indicator comprised of bleachable dye, the bleachabledye is preferably placed on a surface that is placed inside anoxidation-type sterilization chamber. The type of surface on which thechemical indicator is placed depends on the intended purpose or type ofdevice with which the chemical indicator integrates.

The chemical indicator comprises a material having a section ofbleachable dye thereon. The bleachable dye, as described, may beincorporated with a number of different devices, such as a stand alonechemical strip, a self-contained biological indicator incorporating achemical indicator, a challenge pack, a test pack, tape or stickers,pouches, a limited re-use monitor, a warranty indicator, atamper-evident device, and a documentation record (instrument countsheet).

The embodiments of the chemical indicators described herein provides forthe chemical indicator to be placed inside a sterilization chamber withthe medical devices that are being sterilized. The chemical indicator,having bleachable dye thereon, is also placed within the sterilizationchamber. The chamber is sealed and the cavity within filled with agaseous oxidation type sterilant. The sterilant remains sealed withinthe chamber for a time sufficient for the gaseous sterilant to rendermicroorganisms harmless. The sterilant within the chamber contacts thedyed surface of the chemical indicator. While in contact, an oxidationprocess occurs thereby changing the color of the dyed surface toindicate exposure to the sterilant.

After an adequate sterilization period, the sterilant is evacuated fromthe chamber and the chemical indicator is examined. If the indicator haschanged color, sterilant has been introduced into the chamber. Todetermine that the bacteria were inactivated, a biological indicator mayalso be placed within the chamber during the sterilization process, andlater tested, using a culture, for potentially viable bacterial spores.Conversely, if the chemical indicator has not changed color, it can beinferred that the chemical indicator was not exposed to sterilant.

The process just described is applicable for single use chemicalindicators such as chemical indicator strips, a self-containedbiological indicator incorporating a chemical indicator, a challengepack, a test pack, tape or stickers, pouches, tamper-evident devices,and documentation records (instrument count sheets), as well as limitedre-use indicators and warranty indicators.

Response of Indicator to Partial Cycle Conditions

A chemical indicator having bleachable dye in an embodiment of a teststrip was exposed to an oxidation-type sterilant and monitored for colorresponse. The exposure time for the bleachable dye chemical indicatorwas reduced from the standard 50 minutes to 25 minutes thereby providinga difficult test for the chemical indicator.

25 Minute Test

A test was performed in a STERRAD® 100 Sterilizer using a partial cycletime of 25 minute diffusion and 15 minute plasma, at a concentration of6 mg of hydrogen peroxide per liter using a simulated heavy load.Reducing the diffusion time from the standard 50 minutes to 25 minutesprovides less time for the sterilant to reach the chemical indicator andless time for the sterilant to bleach the dye. Thus, this test providesa rigorous test of the bleachable dye chemical indicator.

As is known by those of ordinary skill in the art, various materialsabsorb more sterilant than other items. By way of example, polyurethaneabsorbs more sterilant than latex. The more sterilant that the medicalinstruments absorb, the less sterilant is available to reach the otherareas of the chamber. Thus, test conditions mimicking a heavy load areconfigured to simulate actual conditions such as when the chamber isfull of medical instruments that are partly comprised of materials whichabsorb the sterilant.

Four test pack configurations were used to test the chemical indicatorof the present invention. The first test configuration was a stand aloneconfiguration comprising a chemical indicator strip without anydiffusion barriers. The second test configuration was a double pouchedtest configuration comprising a chemical indicator strip in acommercially available Mylar-Tyvek sterilization pouch. The third testconfiguration, illustrated in FIG. 2, was a biological indicator testpack (BITP) with a latex sample. The fourth test configuration was aBITP with a polyurethane sample. Polyurethane absorbs a large amount ofsterilant thus making the fourth test configuration the mostchallenging.

Upon exposing the test configurations described above to the parametersof the test, each of the bleachable dye chemical indicators successfullychanged from the color red to a yellow/gold color after a single processwithin the sterilization chamber thereby indicating adequate sterilantexposure.

Other Tests

The chemical indicators described herein underwent other testing. Thetesting was performed on a chromate conversion coated aluminum 5052alloy chemical indicator made in accordance with the above describedprocess. The tests reveal distinct advantages over the chemicalindicators of the prior art.

Toxicity Tests

Toxicity tests on processed and unprocessed chromate conversion coatedaluminum alloy base chemical indicator containing metallic azo dye wereperformed in accord with an in vitro biocompatibility study, based onthe International Organization for Standardization (ISO 10993-5)guidelines to determine the potential for cytotoxicity from bleachablesextracted from the material. The test extracts showed no evidence ofcausing cell lysis or toxicity. Thus, a further advantage of thechemical indicator of the present invention over the prior art is thecomplete lack of toxicity of the dye once impregnated or containedwithin the surface of the indicator.

Thus, another advantage of the metallic azo dye, metallic surfacecombination is the stability and lightfastness of the dye in the surfaceof the metal. Certain chemical indicator substances of the prior artwere prone to washing out or to leaching from the surface of thechemical indicator. This can undesirably result in inaccurate readingsand possible contamination of the medical devices. Since the dye asdescribed herein is permanently bonded with the anodization or chromateconversion layer, the dye contained therein does not wash or rinse out.

Temperature/Humidity Resistance

Preliminary stability data for the aluminum chemical indicator show thatthe chemical indicator maintains its original color for at least threemonths when stored at 23° C. at 50% relative humidity, at 30° C. at 50%relative humidity, at 40° C. at 75% relative humidity, or at 50° C. withno relative humidity control. Based on the stability data at 50° C. andthe fact that the rate of chemical reactions generally double for every10° C. increase in temperature, it can be predicted that the aluminumchemical indicator will maintain its original color for at least 12months if stored at 30° C. The present invention's stability is adistinct advantage over the prior art.

Photo Resistance

When exposed to a 30 watt fluorescence light at a distance of less thantwo feet at ambient conditions an unprocessed chemical indicator, asdescribed above, maintained its original color for at least two monthsduring an ongoing test. Furthermore, the aluminum chemical indicatormaintained its processed color when exposed to a 30 watt fluorescencelight at a distance of less then two feet at ambient conditions.

Acid and Base Resistance

As shown in Table 1 below, aluminum chemical indicators maintain theircolor when exposed to vapors from strong acids and strong bases atambient conditions. Chemical indicators of the prior art which useCrystal Violet dye undesirably show a reversal in color under the sameconditions.

TABLE 1 Prior Art Chemical Aluminum Chemical Test Conditions IndicatorIndicator Unprocessed CI exposed to Color Change No Change Strong AcidUnprocessed CI exposed to Color Change No Change Strong Base

Furthermore, the Aluminum Bordeaux RL dye of the embodiment disclosedherein maintains its color (red) in an aqueous solution having pH valuesof 1 to 14.

Steam Sterilization

A chemical indicator was exposed to a steam sterilization process in onetest and exposed to an injection of water into the STERRAD SterilizationSystem in another test. The chemical indicator of the present inventiondid not change color. Thus, steam and water does not cause the color ofthe chemical indicator to change. This is a further advantage over theprior art which would often provide a false reading, i.e. change color,when exposed to steam or water.

Based on the testing detailed above, the claimed invention satisfies thereliability, selectivity, and stability requirements recommended by theAssociation of Advancement of Medical Instrumentation.

Alternative Embodiments

Several embodiments of the claimed invention are contemplated anddescribed below. These are listed by way of example only, as theinvention claim herein is intended to cover all applicationsincorporating the oxidation-type sterilant sensitive dyes.

Chemical Indicator Strip

In one preferred embodiment, a chemical indicator is formed usingbleachable dye by placing the bleachable dye on a strip of material toform a chemical indicator strip. Indicator strips comprise generallysmall pieces of material having a chemical indicator section thereon.The chemical indicator strip is placed in a sterilization chamber andthereby exposed to an oxidation-type sterilant. Upon exposure forsufficient time to the sterilant, the chemical indicator portion of thestrip changes color.

Chemical indicator strips are made in a way which is standard forapplying dye to a strip of material. The bleachable dye may be sprayed,pressed, silk-screened, embedded, or brushed onto the strip. One ofordinary skill in the art is aware of the method of applying dye to amaterial, such as paper, plastic or metallic surface so the process isnot described in detail herein. The chemical indicators may be placed ina sterilization chamber alone or as part of test pack or challenge pack,described below.

Self-Contained Biological Indicator

The chemical indicator of the claimed invention may also be integratedwith a self-contained contained biological indicator. Self-containedbiological indicators are described in detail in U.S. Pat. No. 5,405,580to Palmer entitled Self-Contained Biological Indicators which isincorporated by reference in its entirety herein. FIG. 1 illustrates aself-contained biological indicator (SCBI) 10 integrating a chemicalindicator having bleachable dye. The SCBI 10 comprises a semi-rigidcontainer portion 12 and a cap section 14. Inside the container portion12 are bacterial spores 18. Upon successful exposure to a sterilant thebacterial spores should be inactivated and may be tested to determine ifthe sterilization process was successful. However, determining if thebacterial spores are no longer viable requires that a culture be grown.To reduce the number of cultures which must be grown, a chemicalindicator is incorporated with the SCBI thereby providing an inexpensiveindication that the biological matter was exposed to a sterilant. If thechemical indicator does not indicate exposure to sterilant, then thebacteria within the biological indicator was not adequately exposed tosterilant and the time and expense of growing a culture may be avoided.

The cap section 14 contains a surface 20 containing bleachable dye. Theindicator surface 20 may comprise a circular section on the top of thecap 14, as shown, or alternatively, the entire cap 14 or any section ofthe cap 14 or container portion 12, may be comprised of a materialhaving bleachable dye thereon.

Alternatively, the container portion 12 may further house a glass vialcontaining a growth medium which, when broken by squeezing or pinchingon the outer wall of the container portion 12, places the growth mediumin contact with the bacterial spores 18. The growth medium indicates bycolor change the presence of viable spores.

In use, the one or more self-contained indicators 10 are placed in asterilization chamber or other similar device, the chamber sealed andfilled with gaseous sterilant. If the sterilant successfully enters thechamber for a sufficient period of time the chemical indicator havingbleachable dye will change color. If the bleachable dye changes colorthen the biological material 18 may be used to grow a test culture.However, if the chemical indicator did not change color then the cultureneed not be grown.

Challenge Pack/Test Pack

In another embodiment, the chemical indicator is incorporated with achallenge pack or a test pack. A test pack is used for the routinemonitoring of the sterilization process, and simulates a “worst case”load. A challenge pack is intended to create a somewhat greaterchallenge to the sterilization process than the test pack or the loaditself, and is used to validate a sterilizer upon installation or atregular intervals. Both a challenge pack and a test pack may contain abiological indicator and/or chemical indicator and have a structurewhich limits the movement of the gas accessing the indicators tomovement by diffusion. FIG. 2 illustrates one preferred embodiment of atest pack 50. The test pack 50 has a base 52 formed with one or moreinner depressions 56 with each depression gaseously connected bychannels 58 to the other depressions and the volume outside the testpack.

A cover 54 rests on top of the base. The cover 54 has adhesive on someareas of its lower surface to secure and seal the cover to the base 52.Preferably the cover 54 is transparent thereby allowing items containedwithin the depressions 56 to be seen.

Located inside the test pack 50 is a piece of material, known as asterilant absorber 60, a biological indicator package 62, and a chemicalindicator strip 64. The sterilant absorber, usually polyurethane tubingor latex tubing, helps simulate actual test conditions by absorbing someof the oxidant. The biological indicator package 62 contains bacteriawhich may be in the form of spores. The chemical indicator strip 64contains a section having bleachable dye.

In operation, the test pack 50 is exposed to an oxidation-typesterilant. Through diffusion the gaseous sterilizer enters the test packthrough the channels 58 and thereby encounters the sterilant absorber60. The sterilant absorber 60 absorbs some of the sterilant while theremaining sterilant flows to the other volumes of the depressions 56 ofthe test pack base 52. Eventually the gas comes in contact with thechemical indicator strip 64 and the biological indicator package 62.

Upon completion of the sterilization process, the test pack 50 isremoved from the sterilization chamber and the chemical indicator strip64 inspected for color change. If the chemical indicator strip 64 haschanged color, i.e. the bleachable dye thereon has been bleached by theoxidation-type sterilant, then the sterilant has reached the innervolumes of the test pack for a sufficient amount of time and insufficient concentration to warrant examination of the biologicalindicator package 62. Conversely, if the chemical indicator has notchanged color then the sterilization process is not complete and shouldbe repeated.

Tape and Other Tamper-Evident Devices

In another embodiment, the bleachable dye is incorporated into atamper-evident device for sterilization containers. FIG. 3 illustrates asterilization container. The sterilization container comprises a base300 and a lid 304 having a number of openings 302 with filters (notshown) which allow sterilant to enter the sterilization container whilepreventing contaminants from entering. The base 300 and the lid 304 areconfigured to fit together to thereby form a seal between the base andthe lid. Connected to the lid 304 is a clasp 310 which is configured toengage rods 314. Each rod 314 extends from a latch 316 on the base 300.Opening the latch 316 moves the rod 314 which in turn releases the clasp310 to thereby facilitate removal of the lid 304.

A tamper-evident device 306 is used to provide evidence that thecontainer has not been opened since sterilization. The tamper-evidentdevice 306 possesses a pin 312 which is placed through the latch 316.The pin 312 secures to the opposite end of the tamper-evident devicesuch that when the pin is secured it may only be removed by breaking thepin. When the pin 312 of the tamper-evident device 306 is in the latch316 the latch can not be opened and consequently the lid can not beremoved. Thus, the tamper-evident device and in particular the pin 312must be removed from the latch 316 before the latch will open. Thetamper-evident device 306 also contains a chemical indicator 308comprising a non-pH-sensitive bleachable dye to indicate exposure to anoxidation type sterilant or disinfectant.

In operation, the base 300 contains medical devices in need ofsterilization. The lid 304 is placed over the base 300 so that the clasp310, rods 314, and latch 316 may be engaged to thereby secure the lid tothe base. Next, the pin 312 of the tamper-evident device 306 is placedin the latch 316 and secured to the opposite end of the tamper-evidentdevice. The container and medical devices within are placed within ansterilization chamber and exposed to sterilant for a sterilizationcycle. During the sterilization cycle, the sterilant enters thecontainer through the openings 302. When the container exits thesterilization chamber, the chemical indicator portion 308 of thetamper-evident device 306 is inspected to determine if the chemicalindicator was exposed to sterilant. If exposed to sterilant the chemicalindicator 308 changes color. The pin 312 of the tamper-evident device306 remains within the latch 316 until the time of use for the medicalinstruments. Advantageously, the chemical indicator 308 on thetamper-evident device 306 indicates whether the sealed sterilizationcontainer has been exposed to sterilant, and if not broken, thetamper-evident device indicates that the container has not been opened,i.e. not exposed to outside contaminants. Furthermore, thenon-pH-sensitive chemical indicator will not change color if exposed toan acid or base which would cause a false reading.

In yet another embodiment and as illustrated in FIG. 4, bleachable dye402 resides on tape or a similar flexible medium 400 having adhesive 404on one side. The flexible medium 400 may comprise, but is not limited totape, stickers, or labels. On the side opposite the adhesive 404 isbleachable dye 402. The bleachable dye 402 may be sprayed, screenprinted, rolled, or embedded, into or onto the tape or flexible medium400. Advantageously, the dye 402 may be placed on the tape in the formof letters to provided directions for the operation of the dye or acolor key to remind of the operation of the dye. An indicator tape whichuses pH-sensitive dye which is presently available is STERRAD® ChemicalIndicator Tape available through Advanced Sterilization Products locatedin Irvine, Calif. The Instructions for Use for the STERRAD® ChemicalIndicator Tape are hereby incorporated by reference in their entiretyherein.

In operation, the medical instrument is wrapped using a folding pattern,although other wrapping techniques are available, in a protective wrapor fabric. One such wrap is known by those of ordinary skill in the artas nonwoven sterilization wrap or, in particular, Kimberly ClarkSpunguard which allows the sterilant to pass while preventing airbornecontaminants such as dust and bacterial from depositing on the medicalinstrument wrapped therein. Once the medical instrument is wrappedwithin the protective fabric, the tape having the bleachable dye thereonsecures the protective fabric to ensure that the fabric does not unfoldor unwrap to expose the medical instrument. The taped package is thenplaced in a sterilization chamber to undergo a sterilization process.When the process is complete the wrapped instrument is removed from thechamber and the tape is inspected. The bleachable dye on the tape shouldhave changed color and now acts as a permanent, nonreversible indicationthat the instrument wrapped within is sterile. The medical instrumentremains wrapped within the fabric until ready for use in a medicalprocedure. At the time of use, the tape is torn, not pealed, and theinstrument wrapped therein removed for use. Advantageously, the tapehaving bleachable dye allows health care providers to differentiateprocessed from unprocessed items.

Indicator for Limited Re-Use Instrument

A further embodiment of bleachable dye as a chemical indicator inoxidation-type sterilization processes is to configure the dye to changecolor after a predetermined and specified number of exposures to oxidantsterilization processes where the process is for a known period of timeand a known oxidant concentration. In this configuration the bleachabledye is ideally used as a limited re-use indicator for medicalinstruments having a specified lifetime or designed for a limited numberof procedures. To determine when an instrument or device has exceededits intended number of uses, a surface having bleachable dye thereon ismanufactured to change color after being exposed to the oxidation-typesterilant a number of times which the product or device was designed tobe used. The surface is then placed on the medical instrument so thateach time the medical instrument is used, i.e., for each and every use,the surface is also exposed to the sterilant. Alternatively, the surfacemay be made as an integral surface of the instrument or an attachablesection. Making the surface having bleachable dye an attachable sectionto the medical instrument provides a different lifetime indicator for aninstrument depending upon which bleachable dye surface is attached. Forexample, an instrument may have a lifetime of 30 uses when new and only20 uses thereafter between rebuilding. A surface having bleachable dyecould be attached accordingly to change color when the appropriatenumber of uses has been exceeded.

Warranty Indicator

In yet another embodiment, a warranty indicator is provided using thebleachable dye of the present invention. A warranty indicator is anindicator which provides notice when the warranty of a device is stillin effect, or, conversely, when the warranty is expired. Advantageously,the warranty indicators of the present invention utilize bleachable dyeto provide fast, reliable or undisputable notice when the warrantyperiod is no longer in effect. Furthermore, the warranty indicator ofthe present invention advantageously provides notice of warrantyvalidity or expiration not based on time period from purchase, but basedupon the number of uses of the instrument or device. Warranting aproduct based on the number of uses instead of the time of purchaseeliminates the inequity arising between products that may only be usedonce a year in comparison to products that are used hundreds of timeseach year.

The warranty indicator operates using the same principles as the limitedre-use indicators described above. However, the dye and surface areconfigured such that the number of exposures before color change isidentical to the number of uses for which the product is warranted.

Other Embodiments

It is further contemplated that non-bleachable dye could be used inconjunction with the bleachable dye to display a color key therebyproviding visual color comparison to determine when the bleachable dyehas sufficiently changed color and which color indicates an unsterilizedstate and which color indicates a sterilized state.

It is also contemplated that the bleachable dye may be incorporated withfabric of the type worn by medical professional or of the type describedabove for use with the chemical indicator tape that will be exposed to asterilization process using an oxidant. The dye would be impregnatedinto the fabric to indicate full exposure to a sterilant.

In yet another embodiment, the bleachable dye is incorporated with acount sheet. A count sheet comprises a medium which may be marked uponto record the number and type of medical instruments in thesterilization chamber. A count sheet embodied with bleachable dyethereon would thus record the contents of a sterilization chamber andprovide notice that an oxidative-type sterilant entered the chamber. Thecount sheet could be made up of the type material disclosed herein forother embodiments.

Also within the scope of the invention described herein are othermethods and means of exposing the claimed chemical indicators tooxidation-type sterilants. Devices other then the sterilization chamberdescribed herein may be used to provide the sterilizing agents tomedical instruments and chemical indicators.

It will be understood that the above described arrangements of apparatusand the methods derived therefrom are merely illustrative ofapplications of a number of preferred embodiments and it is not intendedto limit the scope of the invention to the particular forms set forth,but on the contrary, it is intended to cover such alternatives,modifications and equivalents as may be included within the spirit andscope of the invention as defined by the claims.

What is claimed is:
 1. An apparatus for determining exposure to anoxidation-type sterilant or disinfectant, said apparatus comprising: abiological indicator for determining the effectiveness of exposure tothe oxidation-type sterilant; and a chemical indicator for indicatingexposure to the oxidation-type sterilant, wherein said chemicalindicator comprises: a metallic surface; and non-pH sensitive indicatormeans on said surface for indicating exposure to the oxidation-typesterilant.
 2. The apparatus of claim 1, wherein said indicator means isan azo dye.
 3. The apparatus of claim 1, wherein said indicator means isa permanent indicator means.
 4. The apparatus of claim 1, wherein saidsurface comprises anodized aluminum.
 5. The apparatus of claim 1,wherein said surface comprises a chromate conversion coating.
 6. Theapparatus of claim 1, wherein said biological indicator is aself-contained biological indicator.
 7. The apparatus of claim 6,wherein said chemical indicator comprises a generally flat disk on saidself-contained biological indicator.
 8. The apparatus of claim 1,further comprising a test pack, wherein said test pack is configured toprovide for gas flow into said test pack by diffusion and wherein saidchemical indicator and said biological indicator are inside said testpack.
 9. The apparatus of claim 1, wherein said apparatus comprises acontainer having a cover, wherein said cover is secured to saidcontainer with a tamper-evident device and wherein said tamper-evidentdevice has said surface with said non-pH sensitive bleachable dyethereon.
 10. The apparatus of claim 1, wherein said metallic surfacecomprises a flexible medium having said indicator means on at least afirst surface of said flexible medium.
 11. The apparatus of claim 10,further comprising adhesive on a second surface of said flexible medium.12. The apparatus of claim 1, further comprising a warranty indicatorwhich provides notice when a warranty of said apparatus is still ineffect.
 13. The apparatus of claim 1, wherein said oxidation-typesterilant comprises hydrogen peroxide.
 14. The apparatus of claim 13,wherein said oxidation-type sterilant comprises aqueous hydrogenperoxide.
 15. The apparatus of claim 13, wherein said oxidation-typesterilant comprises hydrogen peroxide vapor or gas.
 16. An apparatus fordetermining exposure to an oxidation-type sterilant or disinfectant,said apparatus comprising: a biological indicator for determining theeffectiveness of exposure to the oxidation-type sterilant; and achemical indicator for indicating exposure to the oxidation-typesterilant, wherein said chemical indicator comprises: a metallicsurface; and non-pH sensitive indicator means permanently bound on saidsurface for indicating exposure to the oxidation-type sterilant.
 17. Anapparatus for determining exposure to an oxidation-type sterilant ordisinfectant, said apparatus comprising: a biological indicator fordetermining the effectiveness of exposure to the oxidation-typesterilant; and a chemical indicator for indicating exposure to theoxidation-type sterilant, wherein said chemical indicator comprises: ametallic surface; and non-pH sensitive indicator means on said metallicsurface for indicating exposure to the oxidation-type sterilant, whereinat least a portion of said metallic surface is on the outside of acontainer within which said biological indicator is housed.